1. Field of the Invention
The present invention relates to a safety running system for a vehicle for preventing a subject vehicle from coming into contact with an oncoming vehicle on an adjacent lane of the road for opposite traffic by using an object detection unit such as a radar device.
2. Description of the Related Art
A safety running system for a vehicle as described above is well known in the official gazette of Japanese Patent Unexamined Publication (Kokai) No. HEI 7-14100.
The safety running system disclosed in the above official gazette is adapted to avoid a collision of a subject vehicle with an oncoming vehicle on an adjacent lane of the road for opposite traffic by generating an alarm to the driver of the subject vehicle to make the driver perform a voluntary collision avoidance operation or automatically applying the brakes of the subject vehicle in the event that the subject vehicle enters the adjacent lane for opposite traffic to thereby encounter a possible collision with the oncoming vehicle on the same lane.
As shown in FIG. 3, a transverse travelling distance Y.sub.1 of the subject vehicle Ai from the vehicle body axis thereof is calculated from a future travelling locus of the subject vehicle Ai estimated based on the vehicle velocity Vi and yaw rate .gamma.i thereof. Further, a relative transverse distance Y.sub.2 from the vehicle body axis of the subject vehicle Ai to the oncoming vehicle Ao is calculated with a radar device. And, a collision possibility of the subject vehicle Ai with an oncoming vehicle Ao on an adjacent lane for opposite traffic is judged by comparing the transverse travelling distance Y.sub.1 with the relative transverse distance Y.sub.2.
As shown in FIG. 14, however, in a case where the driver of the subject vehicle Ai tries to overtake a preceding vehicle Af, the driver first steers the steering wheel rightward to change the path of movement of the vehicle to the right-hand side of the road (in the case of left-hand side traffic) and then steers it back leftward to return to the original path of movement of the vehicle or the left-hand side lane after the driver's vehicle Ai has over taken the preceding vehicle Af. Due to this, with the safety running system described in FIG. 3, there is caused a problem that a possible collision of the subject vehicle with an oncoming vehicle Ao is erroneously judged as occurring as soon as the steering wheel of the subject vehicle is steered rightward even when in reality there is no such collision possibility.
Further, as shown in FIG. 13, when a subject vehicle Ai approaches an end of a rightward curve in a left-hand side traffic road, since the driver steers the steering wheel leftward to enter a straight path from the curved path, an actual transverse travelling distance becomes shorter than an estimated transverse travelling distance Y.sub.1. As a result of this, a judgement is made that there is a collision possibility when in reality there is no such collision possibility, this triggering the performance of an unnecessary collision avoidance control, thereby causing a risk of the driver feeling a physical disorder.
Moreover, the aforementioned conventional safety running system is adapted to judge a possible collision with an oncoming vehicle by estimating a deviation of a subject vehicle to an adjacent lane of the road for opposite traffic. Therefore, this deviation to an adjacent lane of the road for opposite traffic is determined in accordance mainly with the azimuth of the travelling subject vehicle (an angle formed by the vehicle body axis of the subject vehicle and the center line of the road). Due to this, for instance in a case where the subject vehicle is steered so as to avoid an obstacle on the road side, an erroneous judgement of a collision possibility is made only when the azimuth of the travelling subject vehicle is temporarily directed to the side of the adjacent lane for opposite traffic, and therefore there is caused a problem that every time such an erroneous judgement is made, an unnecessary collision avoidance control is performed to make the driver feel troublesome.